High-entropy alloys (HEAs) are the focus of current research for their diverse properties, including superconductivity and structural polymorphism. However, the polymorphic transition has been observed only in non-superconducting HEAs mostly under high pressure. Here we report the discovery of the superconductivity and temperature-driven polymorphism in (V_0.5Nb_0.5)_3−xMo_xAl_0.5G_0.5 (0.2 ≤ x ≤ 1.4) HEAs, which are of a single body-centered cubic (bcc) structure for x = 0.2 and a mixture of the bcc and A15 structures for higher x values. Upon annealing, the bcc structure undergoes a polymorphic transformation to the A15 one and all HEAs exhibit bulk superconductivity. For the sample with x = 0.2, the bcc polymorph is not superconducting down to 1.8 K, whereas the A15 polymorph has a superconducting transition temperature T_c of 10.2 K and estimated zero-temperature upper critical field B_c2(0) of 20.1 T, both of which are the highest among HEA superconductors. With increasing Mo content x, both T_c and B_c2(0) of the A15-type HEAs decrease, yet the large ratio of B_c2(0)/T_c signifies a disorder-induced enhancement of the upper critical field over a wide x range. The decrease in T_c is attributed to the decrease in both the electronic specific-heat coefficient and electron-phonon coupling strength. Furthermore, the valence electron count dependence of T_c, which is different from both the binary A15 and other structurally different HEA superconductors, suggests that T_c may be increased further by reducing the number of valence electrons. Our results not only uncover HEA superconductors of a new structural type, but also provide the first example of polymorphism-dependent superconductivity in HEAs.

高熵合金（HEA）由于其多种特性（包括超导性和结构多态性）而成为当前研究的重点。但是，仅在非超导HEA中大部分在高压下才能观察到多晶型转变。这里，我们报告的超导电性在（V发现和温度驱动多态性_0.5的Nb _0.5）_{3- X}沫_X的Al _0.5 G ^ _0.5（0.2≤ X ≤1.4）HEA与，这是一个单一的体心立方（BCC）的结构为X = 0.2和BCC的混合物和A15结构更高的X价值观。退火后，bcc结构经历了向A15的多晶型转变，所有HEA均显示出本体超导性。对于x = 0.2的样品，bcc多晶型物不会在低至1.8 K时超导，而A15多晶型物的超导转变温度T _c为10.2 K，估计的零温度上临界场B _c2（0）为20.1 T，两者均是HEA超导体中最高的。随着Mo含量x的增加，A15型HEA的T _c和B _c2（0）均降低，但B _c2（0）/ T _c的比例较大。表示在较大的x范围内无序诱导的上临界场增强。在减少Ť _Ç归因于在电子比热系数和电子-声子耦合强度都降低。此外，与二元A15和其他结构不同的HEA超导体均不同的T _c的价电子数依赖性表明，可以通过减少价电子数来进一步提高T _c。我们的结果不仅揭示了一种新的结构类型的HEA超导体，而且还提供了HEA中依赖多态性的超导性的第一个示例。